1. Field of the Invention
This invention relates to a magnetoresistance effect head provided with a spin valve film.
2. Description of the Related Art
Generally, the reading of information recorded in a magnetic recording medium is accomplished by a method which comprises imparting a relative motion between a magnetic read head furnished with a coil and the recording medium and detecting the voltage induced electromagnetically in the coil in consequence of the relative motion. It has been known to attain the reading of information otherwise by the use of a magnetoresistance effect head (hereinafter referred to as "MR head") [refer to IEEE MAG-7,150 (1971), for example].
The MR head operates by virtue of the phenomenon that the electric resistance of a certain kind of ferromagnetic body varies with the intensity of an external magnetic field and has already found recognition as a highly sensitive head usable for a magnetic recording medium. In recent years, the trend of magnetic recording media toward decrease in size and increase in capacity has been resulting in a growing decrease of the relative speed between the magnetic read head and the magnetic recording medium during the course of the reading of information. Under the circumstances, the expectation of a MR head which is capable of deriving a large output even at a small relative speed has been swelling.
Heretofore, the so-called Permalloy, i.e. a Ni-Fe alloy, has been used for the part of a MR head which senses an external magnetic field and varies the resistance of itself in response thereto (hereinafter referred to as "MR element"). The Permalloy type alloys, however, are such that the rates of change of magnetoresistivity thereof are up to about 3% at most even when they are possessed of ideal soft magnetic properties. For the MR element in the magnetic recording medium which has undergone decrease in size and increase in capacity, therefore, the Permalloy type alloys offer no sufficient rate of change of magnetoresistivity. Thus, the desirability of developing a material displaying highly sensitive magnetoresistivity fit for a MR element has been finding widespread recognition.
In answer to the demand for an ideal MR element material, it has been ascertained that the so-called artificial lattice film, i.e. a multilayer film obtained by alternately superposing ferromagnetic metal films and nonmagnetic metal films such as, for example, Fe/Cr or Co/Cu, under certain conditions fit for the purpose of antiferromagnetically coupling adjacent ferromagnetic metal films in the laminate, exhibits gigantic magnetoresistance effect. The observation of an artificial lattice film displaying a large ratio of change of magnetoresistance change ratio exceeding even the maximum of 100% has been reported (refer to Phys. Rev. Left., Vol. 61, 2474 (1988) and Phys. Rev. Left., Vol. 64, 2304 (1990), for example). The artificial lattice films, however, are unfit for MR elements because of their unduly high saturation magnetic fields.
The fact that large magnetoresistance effect is realized with a multilayer film of the sandwich construction of ferromagnetic film/nonmagnetic film/ferromagnetic film in spite of the absence of an antiferromagnetic coupling of adjacent ferromagnetic films has been reported. Specifically, one of the two ferromagnetic films opposed to each other across an interposed nonmagnetic film is magnetized fast by means of an exchange bias and the other ferromagnetic film is magnetically inverted by means of an external magnetic field. As a result, large magnetoresistance effect is obtained in the multilayer film by changing the relative angle of the directions of magnetization of the two ferromagnetic films opposed to each other across the nonmagnetic film. The multilayer film of this type is called a spin valve film (refer to Phys. Rev. B., Vol. 45, 806 (1992), J. Appl. Phys., Vol. 69, 4774 (1991), for example). Though the spin valve films have smaller magnetoresistance change ratio than the artificial lattice films, they fit MR elements because they are magnetized to saturation in a low magnetic field. The MR heads using these spin valve films have a very bright prospect of justifying their utility in practical applications.
Incidentally, in the spin valve film which has the sandwich construction, its magnetoresistance change ratio depends to a great extent particularly on the thickness of the magnetic layer formed of ferromagnetic films because the part thereof in which the magnetoresistance effect manifests itself has a small total film thickness and the scatter of electrons on the surface of MR element contributes greatly to the occurrence of the phenomenon. In the manufacture of a MR effect head using the spin valve film, therefore, the selection of a material for the magnetic layer and the setting of thickness of the film prove to be important. No specific guideline, however, has been drawn to date with respect to the material of the magnetic layer and the thickness of the film. Under the circumstances, therefore, a spin valve film construction which is capable of manifesting large magnetoresistance change ratio with satisfactory repeatability remains yet to be developed. The MR head using a spin valve film has not yet been developed enough to justify its utility in practical applications.
In the meantime, the magnetic recording media have been rapidly advancing in terms of the growth of recording density and the exaltation of linear recording density has been advancing proportionately. To attain effective reading of signal magnetic fields, the MR head must be possessed of enhanced linear resolution. In the MR head of the popular shield type, the linear resolution can be heightened by decreasing the distance (gap) between the shield layer and the MR element. When the decrease of the gap is exclusively resorted to, however, the rate of change of magnetic resistance offered by the spin valve film is inevitably impaired. Thus, the desirability of developing a MR element using a spin valve film which displays improved linear resolution and, at the same time, produces a large magnetoresistance change ratio with high repeatability has been finding widespread recognition.